As is known in the art, Worldwide Interoperability for Microwave Access (WiMax) uses Unsolicited Grant Service (UGS) in order to ensure the Quality of Service (QoS) of a Voice over Internet Protocol (VoIP) call. In WiMax, predetermined bandwidth resources are assigned through UGS.
For the purpose of UGS associated services, a mobile station such as an Integrated Access Device (IAD) is assigned an initial radio resource through a net entry process. The net entry process is designed to set bandwidths for UGS associated services by performing DSA_REQ/DSA_RSP procedures.
In the net entry process realized up to present, one UGS service is connected by one DSA_REQ/DSA_RSP procedure. When the mobile station attempts to use three channels, the DSA_REQ/DSA_RSP procedure has to be performed three times for forward and backward directions.
In the case of VoIP environment, a voice codec, which is initially negotiated with a counterpart station, can be frequently replaced by another voice codec. When a G.711 voice codec using a bandwidth 80 Kbps set to a channel is replaced with a G.729 voice codec using a bandwidth 24 Kbps, the remaining 56 Kbps bandwidth is not used and thus is wasted.
For example, the IAD, to which a plurality of channels (i.e., n number of channels) are assigned, suffers from the waste of radio resources since a bandwidth of n×56 Kbps is not used.
Conversely, when a G.729 voice codec using a 24 Kbps bandwidth set to a channel is replaced with a G.711 voice codec using a 80 Kbps bandwidth, QoS cannot be ensured due to a narrow transmission/reception bandwidth.